It's a much smaller battery, but remember that it must power full-time live view.

Do no actual miniaturization really, just start with the current Rebel & hybrid sensor and get your size savings from the short register, no mirrorbox, no VF, tiny battery...

The 650D/T4i is already fairly small for a DSLR. What other way would you "miniaturize" a digital camera, except to leave off those bulky items? Have you seen inside an EOS-M to be so sure that the circuit boards etc are not smaller? The M dimensions are significantly smaller than the 650D even allowing for the mirror/pentamirror/OVF/PDAF system. And it has alloy frame, yet is much lighter in weight. And isn't a new smaller lens mount "miniaturization?"